Exhaust gas control in flame ionization detectors

ABSTRACT

Flame ionization detector having a burner inside of a tube, the tube having cover means provided for connection to an exhaust pipe and establishing a collecting chamber for exhaust gases of the burner into which scavenging air is fed at a rate sufficient for diluting the exhaust gases to a significant extent, so that the dew point of the resulting mixture is reduced, and little or no condensation occurs along discharge path for the air exhaust gas mixture.

United States Patent 1 Hofmann Aug. 7, 1973 541 EXHAUST GAS CONTROL IN FLAME 3,473,895 10/1969 3mm at al. 23,253 EF 3,489,523 1/1910 Clardy er al. 23/254 EF x IONIZATION DETECTORS [75} Inventor: Kurt Hofmann, Hergershausen,

Germany Primary Examiner-Morris O. Wolk Assistant Examiner-R. M. Reese [73] Asslgneez Hartmann & Braun, Messund Regeltechnik, Frankfurt, Germany -Mina5%9913995W R &

[22] Filed: Aug. 2, 1971 [21] Appl. No.: 167,998 I [57] ABSTRACT Flame ionization detector having a burner inside of a [30] Foreign Application Pnorny Data tube, the tube having cover means provided'for con- 9 G 70 29 5985 nection to an exhaust pipe and establishing a collecting chamber for exhaust gases of the burner into which [52] US. Cl 23/254 EF scavenging air is fed at a rate sufficient for diluting h [51] h lt. Cl. Goln 31/12 exhaust gases to a significant extent so that the dew [.58] Fleld of Search 23/254 EF, 232 point of the resulting mixture is reduced, and m or no condensation occurs along discharge path for the air [56] References C'ted exhaust gas mixture.

UNITED STATES PATENTS 3,366,456 l/l968 Andreatch et al. 23/254 EF 4 Claims, 1 Drawing Figure 14 K 20 j s/ Z/e cz r/c A 644/ e E v l: l l i 6 5 gii J: /]0

4 4/70 Fz/e/ E 1 (a n /r 0 3 EXHAUST G AS CONTROL IN FLAME IONIZATION DETECTORS The present invention relates to improvements in flame ionization detectors and more particularly to the control of exhaust gas flow from a tubular chamber in such a detector.

In order to discharge exhaust gases from a flame ionization detector and from the housing in which the detector is located, usually there is provided a pipe or tube which leads from the burner chamber, down through the housing and out at the bottom, so that condensation water can likewise flow through the pipe and out. It has been found that occasionally the water coagulates to large drops that may form, up to the point that the entire tubular cross sectionof the pipe is shut. This is, of course, only a temporary disturbance as the increasing pressure within the housing will soon clear the passage, but it is also apparent that the result is a periodic variation in pressure, wherein periods of pressure increase are followed by periods of pressure decrease in alternating sequence, inside of the burner and here particularly within the zone above the flame; operability of the detector is significantly impeded by these pressure variations as the ionization process may vary accordingly.

It is an object of the present invention to improve flow conditions for exhaust gas flow from an ionization detector, and to free these detectors from this particu lar deficiency. In accordance with the preferred embodiment of the present invention, it is suggested that the housing of the detectorbe provided withopenings through which scavenging air can enter for diluting the exhaust gases rising from the burner. Air and exhaust gases mix in a ring or funnel shaped collecting chamber disposed above the burner. The exhaust gases as diluted" by scavenging air leave the housing as usual, but the dew point of the resulting mixture is reduced to such'an extent that condensation of moisture in the exhaust gas is prevented with certainty.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

The FIGURE shows somewhat schematically, and as cross-section view in part, a flame ionization detector improved in accordance with the present invention as far as the exhaust gas flow is concerned.

Proceeding now/to, the detailed description of the drawings, the FIGURE shows a housing 1 with a partic-. ular wall or partition)- to. which is secured a flame ionization detector 3-, The sample gas is fed to the detector 3 via a conduit 4; the fuel or combustible gas is fed. to the detector via a conduit 5, and the air needed for combustion is fed via a line or conduit 6.

The detector includes a burner nozzle 21, that receives the various gases. A pickoff electrode for ionization measurement is depicted. above the flame of burner 21 as being suspended. from the top cover of a pipe 8 that establishes the burner chamber. The top of pipe 8 is provided with apertures 7- leading into an annular collecting chamber/9 which circumscribes the top of pipe 8 Exhaust gases fromthe burner pass through apertures 7 into chamber 9, and an exhaust pipe on conduit 10 leads therefrom to the bottom of housing 1.

On the other side of wall 2 is provided space 11 which contains various parts that are needed additionally for operating the flame ionization detector. These auxiliary components are conventional and are not shown in great detail. Briefly, there is for example the electrical unit 12 that contains power supply as well as electrical equipment providing for'measurement indication and being electrically connected to the electrode in detector 3.

Next, is provided a pneumatic operating unit 13 with pressure indicator 14. The pneumatic operating unit 13 receives air from the outside via connection 15 for purposes of pneumatic control. Unit 13 controls particularly the flow of combustible gas and the flow of air to the burner. Fuel gas and air respectively enter control unit 13 through conduits l6 and 17, and pneumatic control establishes constant rates of flow respectively through the conduits 5 and 6 into the burner. Some of the air that enters the housing through conduit 15' is branched off by a pipe 18 for discharge into the interior of chamber 11. Partitioning 2 has openings 19 leading into chamber 1 that contains the detector, so that air flows into that chamber. This then is the supply of scavenging air needed for operating the improvement in accordance with the invention.

The annular collecting chamber 9 is provided with slots 20 that are annularly arranged, and air will pass through the slots to mix with exhaust gases entering also the collecting chamber but through openings 7. The exhaust gases as flowing into pipe 10 arethoroughly diluted with air providing scavenging operation accordingly. The mixing process in chamber 9 is aided by the fact that exhaust gases and air flow into the chamber along intersecting directions. Moreover, scavenging air flows into chamber 9 from above and from below, the flow circumscribing the flow from openings 7 into the chamber.

The pneumatic control unit 13 may include dehumidifying equipment so that the scavenging air is poor in moisture to begin with. Furthermore, the amount of air that is fed into the collecting chamber 9 per unit time via the path as described is preferably a large multiple of the rate of exhaust gas development, and may be a hundred-fold that quantity, so that the dew point of the mixture leaving chamber 9 via pipe 10 is significantly reduced. Particularly, the reduction is sufflcient in that even rapid cooling of burner gases in chamber 9 and in pipe 10 will not cause precipitation of moisture therein. The dew point will drop to such a low value that there is little or no condensation of water.

Of course, it has to be considered that operating conditions may deteriorate for some reason or another (rough handling, age,etc.). Also, it may occur thatthe control equipmentbecomes faulty, for example, the temperature control for the entire apparatus may fail! Therefore, some water may precipitate in the pipe 10, and again the unwantedv periodic pressure increase in the exhaust system may occur. However, it should be realized that detector operation will hardly'be influenced because the particular inventive exhaust gas system avoids direct connection between exhaust pipe 10 and the flame and burner chamber of the detector. The collecting chamber operates as a pressure buffer and pressure increase in the exhaust system will, in fact, be

noticed in the interior of tube 8 to a very negligible extent only.

It should be mentioned, that the collecting chamber may have different configuration, and be funnel shaped rather than annular. Essential is the providing of a chamber in which scavenging air can mix thoroughly with the exhaust gases of the burner, and that only highly diluted exhaust gas flows into the exhaust pipe such as 10.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.

l claim:

1. In a flame ionization detector having a burner inside of a tube, closed at the top by a cover except for discharge openings in the cover; the tube cover having additional means for establishing a collecting chamber external to the inside of the tube and being connected to an exhaust tube, the collecting chamber receiving exhaust gases from the tube as developed by the burner through the discharge openings and feeding these gases to the exhaust tube; and

external openings in the cover for admitting scavenging air and feeding the scavenging air into the collection chamber at a rate sufficient for diluting the exhaust gases as developed in the burner tube.

2. in a flame ionization detector as in claim 1, the openings for feeding air into the collecting chamber being proportioned so that the rate of air flow greatly exceeds the rate of exhaust gas flow through the discharge openings into the collecting chamber, so that the dew point of the resulting mixture is reduced, there being little or no condensation along discharge path for the air-exhaust gas mixture.

3. In a flame ionization detector as in claim 1, the external openings in the cover being annularv 4. In a flame ionization detector having a bumer'inside of a tube closed at the top by a cover except for discharge openings in the cover, the tube cover having additional means for establishing a collecting chamber external to the inside of the tube and being connected to an exhaust tube, the collecting chamber receiving exhaust gases from the tube as developed by the burner therein, through the discharge openings and feeding these gases to the exhaust tube, the improvement comprising:

external annular openings in the cover circumscribing the said discharge openings for admitting scavenging air and feeding the scavenging air into the collection chamber at a rate greatly exceeding the rate of exhaust gas flow into the collecting chamber for diluting the exhaust gases as developed in the burner tube, so that the dew point of the resulting mixture is reduced, there being little or no condensation along the discharge path for the scavenging air exhaust gas mixture. 

2. In a flame ionization detector as in claim 1, the openings for feeding air into the collecting chamber being proportioned so that the rate of air flow greatly exceeds the rate of exhaust gas flow through the discharge openings into the collecting chamber, so that the dew point of the resulting mixture is reduced, there being little or no condensation along discharge path for the air-exhaust gas mixture.
 3. In a flame ionization detector as in claim 1, the external openings in the cover being annular.
 4. In a flame ionization detector having a burner inside of a tube closed at the top by a cover except for discharge openings in the cover, the tube cover having additional means for establishing a collecting chamber external to the inside of the tube and being connected to an exhaust tube, the collecting chamber receiving exhaust gases from the tube as developed by the burner therein, through the discharge openings and feeding these gases to the exhaust tube, the improvement comprising: external annular openings in the cover circumscribing the said discharge openings for admitting scavenging air and feeding the scavenging air into the collection chamber at a rate greatly exceeding the rate of exhaust gas flow into the collecting chamber for diluting the exhaust gases as developed in the burner tube, so that the dew point of the resulting mixture is reduced, there being little or no condensation along the discharge path for the scavenging air exhaust gas mixture. 